Manufacture of motor fuel



May 16, 1944. F. HoRToN .Er AL MANUFACTUREHOF MOTOR FUEL Filed June 20,1939 Patented May 16, 1944 l I MANUFAOTURE or Moron FUEL Francis Horton,Riverdale, N. Y., Lebbens C. Kemp, Port Arthur, Tex., and Richard E.Nagle, New York, and Loren P. Scoville,'` White PlainaN. Y., assignors,by-mesne assignments, to The Texas Company,'New York, N. Y.,`acorporation of Delaware Application June 20, 1939, Serial No. 280,064

' 12 claims. (ci. esca-683.4)

This invention relates to the manufacture of motor fuel and has to doparticularly with the alkylation of isoparains with olens to producehigh antiknock branch chain parailln` hydrocarbons of gasoline boilingrange. The invention is concerned with the conversion of normallygaseous hydrocarbons into high antiknock gasoline hydrocarbons by thealkylation of low-boiling y isoparafins,such as isobutane orisopentane', with oleflns in the presence of an alkylation catalyst.

The invention contemplates a process for the commercial production ofhigh antiknock motor fuel, for example aviation gasoline, from refinerygases including cracking still gases.

In the alkylation of isobutane with olens, it.

is desirable to treat an unsaturated hydrocarbon mixture containingisobutane in excess of the oleiins. Renery gases such as cracking stillgases generally contain an excess of oleiins and special methods forobtaining a, suitable charge for alkylation are necessary. A phase ofthe invention includes the preparation of a suitable charge to thealkylation operation. n

In the preparation o f the charging stock, cracking still gases or otherrefinery gases or mixtures thereof, are fractionated to obtain a chargesuitable for alkylation with or Without the addition of additional lowboiling isoparafins from another source. For example, gases derived froma cracking still may be--fractionated to remove lighter and heavierconstituents and the remains intermediate cut used as the charge. Thus,by removing propaneon the low side and normal butane and heavier on thehigh side, a middle cut may be obtained of the desired characteristics.Such -an intermediate cut may comprise 'a fractionator or stabilizerside stream which on fractionation or debutanization lproduces asatisfactory charge for alkylation. In case the side stream has a fairLywide boiling range, showing only rough fractionation, then the sidestream may be fractionated to obtain a, rather sharply' fractionatedcut, and thisv cut used as such, or after debutanization to separate aportion of the normal butane.

It is desirable when using a stabilizer side stream to enrich suchvstream, preferably after extraneous light condensate may be anvoverheadfraction from a fractionator or stabilizer, gases from an accumulatordrum of va cracking still, or

an absorption condensate obtained by absorption extraction of variouscracking-still gases.

'I'he light condensate is preferably depropanized prior to mixingthereofwith the side stream.

The mixture of side stream and light condensate is preferablydebutanized, prior to charging the mixture tothe alkylation operation.The debutanizing operation removes al1- or a portion of the normalbutane and thereby increases the ratio of isobutane to loleflns. Byregulating the respective 'proportions of the side stream and the lightcondensate, .a product containing the `de sired ratio of isobutane tooleflns for alkylation is readily secured. It is preferable that thecharge contain a ratio of isobutane to oleiins of at least 1:1 andpreferably a considerable excess of isobutane, for example a, ratio ofisobutane to oleiins within the range of about 2:1 and 7:1, or higher.

Another feature of the invention is an improved type of alkylationoperation. In lthe alkylation operation a stream of isobutane andcatalyst may be circulated through a mixer, a chiller, a reaction zone,and back to the mixer. The

vhydrocarbon charge containing the isobutane'and oleiins is injectedinto this stream. Fresh catalyst may be added to the stream and spentcatalyst withdrawn. In the reaction zone the isobutane is alkylated bythe oleflnsin an exothermic increase the volume of available charge.Such reaction,. and the exothermic heat of reaction is removed in thechiller by refrigeration with a suitable refrigerant, such as propane.

IA further feature of the invention is the treatment or distillation lofthe hydrocarbon alkylation products. The crude alkylate is fractionatedto remove excess or residualnormally gaseous hydrocarbons which arerecycled, at least in part. to the charge fractionation operation. Itispreferable to' debutanize the crude alkylate and'fractionate at leasta portion of theoverheadcut to separate a fraction rich in isobutanewhich may be recycled to the alkylation operation. The remaindercontainingsnormal butane may be returned to the fractionation operationin which the charge is fractionated for depropanization. A preferredmethod of operation is to split the overhead from/the debutanizer,returning one4 portion to the charge fractionator and furtherfractionatin'g the other portion to concentrate the isobutane forrecycling to the alkylation operation. The normal butane which isseparated in the fractionation of the latter portion may be dischargedfrom the system andthe normal butane so discharged may be so regulatedas tobe approximately equal to thenormal butane entering thesystem inthe fresh feed. In this way a balanced operation is obtained whereby anex- I cessivevolun'ie of butane will not build up in the system.

The invention will be more fully understood from the followingdescription read in connection with the accompanying drawing which showsa diagrammatic sketch oi' one form of apparatus for carrying out theprocess of the invention.

l Referring to the drawing, a cracked naphtha, for example from anaccumulator drum of an adjacent cracking still, is passed through a lineI to a stabilizer 2. In this stabilizer a stabilized naphtha is'producedwhich is withdrawn from the bottom thereof' through the line 3. A lighthydrocarbon fractionA containing all or a portion of the C3hydrocarbons, including propane, is

taken overhead through the line 5; A side stream` containing C4yhydrocarbons, with or without any portion of the Cs hydrocarbons, iswith' drawn through the line G. Such a side stream may be relativelyhigh in isobutane content .and contain isobutane in considerable excessof the oleiins. The side stream is forced by the pump 1 through the line8 to a fractionator I0. In the.

fractionator the lighter hydrocarbons, such as all or; a portion of theCa hydrocarbons are re` moved overhead through the line II. The lightfractions taken overhead from the stabilizer 2 through the line 5 andfrom the Iractionator @il through the line l i, are joined and passedthrough ythe line I2 and a condenser ill, wherein the hy- Edrooarbonsare at least partially condensed, and the' resulting condensatecollected in receiver i5. The uncondensed hydrocarbons are removed fromthe top of the accumulator through the line It. The condensate intheaccumulator w, including propane, 'is withdrawn from the bottom thereofthrough the line I and pumped by the pump is through the line i@ to theupper portion of the fractionator Iii, and through the line Y 2l to ytheupper portion of the stabilizer 2. as a refiuiemediurn.. The liquidfraction in the fractionator It, preferably a C4 fraction, is withdrawnfrom the bottom of the fractionator I@ through the line 22 and pumped'by the pump 23 or sent under fractionator pressure without a pumpthrough the line 2@ to a debutanzer 2%, o; may be used direct asalkylation charge by naming it through branch line 26.

A light condensate, such as the lower boiling fractions of a debutanizedcracked naphtha, or

y debutanized absorption condensate, preferably containing C4hydrocarbons and a considerable amount of hydrocarbons boiling somewhatabove C4 and containing isobutane and butylenes in which the butyienesare ordinarily Ain excess oi the isobutane, may be charged through theline 27 and commingled' in the line 22 with the Cr cut withdrawn fromthe bottom of the fractionator It. This light condensate in mixture withthe C4 cut is passed to a debutanizer 2b. In the debutanizer ze, adebutamzed iight: napmha,

preferably containing at least a portion of the normal butano, iswithdrawn from the bottom of the debutanizer through the line 2E. A C4fraction 'containing isobutane in excess of the olens is removedoverhead from the debutanizer through the line 2s and condenser Ill. Inthe condenser the hydrocarbons are liquefied and the condensate forcedby the pump 3i tothe manifold line 32, continunicisttirigA with branchlines 33. 34 and "85 whreby'the. hydrocarbon charge may be split andpassed in multiple injectioninto alkyiation stages I. 2l and 3respectively. A portion of the condensate in line 32 may be returned tothe upper portion of debutanizer 25 as a reux.

The alkylation stages I, 2 and 3 are multiple units and while threestages are shown, it is to be understood that any number may be used.The details of only stage I are shown.

The hydrocarbon charge is passed through branch line 33 to the stagenumber I and is introduced into the line 35 through which is circulated,by the pump 36, a stream of alkylation catalyst, alkylate and isobutane.The mixture is passed through a mixer 31 which may be of any well knownlor preferred type whereby the hydrocarbons are intimately contacted withthe catalyst. The mixture is then passed through the line 3B to achiller 39 wherein the exothermic .heat of reaction is removed by arefrigerating medium passing in indirect contact with the hydrocarbons.-

The refrigerating medium is preferably propane which is introducedthrough the line to a tank 4i. The liquid propane is passed from thebottom of the tank 4I through the line 42 into the chiller 39 whereinthe propane is vaporized thereby eiecting cooling by indirect heatexchange., The vapors passfrom the chiller through the vapor line 43back to the tank 4I. The vapors of propane are removed through the lineit to a compression unit to be oompressed, cooled and .condensed to formliquid propane which may be recharged to the system through the lineil?.

The mixture of catalyst and hydrocarbons the settler 5&3 the catalyst isseparated from the hydrocarbons and is withdrawn through the line soand'rnay be recycled through the line 55. The

hydrocarbons are passed from the settler through the line 56 to thestage 2 of the process which is substantially identical with stage I andis shown diagrammatically. The hydrocarbons from stage 2 are passedthrough the line 51 totage 3. From stage s thehydrocarbons are passedthrough the line 5t to a neutralizer tu, referred to hereinafter.

Fresh catalyst may be introduced into the alhylation stages through theline 61 connecting with branch lines $8, Si! and III whereby the freshcatalyst may be introduced into stages I, il and t respectiveb,preferably into the circulating stream'of hydrocarbons and catalyst. Thespent catalyst may be withdrawn from stages I, 2 and 3 respectivelythrough the lines 1I, 12 and lo, which communicate with a draw-oir line1I. for discharging the spent catalyst from the systeni for recovery orother disposal.

In the amlation units just described, the circulating streams oi'hydrocarbon and catalyst contain a ratio ofcatalyst to hydrocarbon oiabout 1:1 by volume. The catalyst is preferably sulfuric acid 0i' about9o to 100% strength, al-

though other suitable liquid catalysts are co'ntemplated. such ashydrated boron trliiuoride. A

very high ratio of circulated hydrocarbon to fresh .hydrocarbon ismaintained. The ratio may range between about 5:1 and 100:1 andpreferably between about` 10:1 and 30:1.

In the neutralizar $9,v the hydrocarbons are bons are pumped from theneutralizer 60 through.

the line. by the pump to a debutanizer 85. The overhead from thedebuntanizer 85. containing isobutane and all or a portion ofthev normalbutane, is passed through line 18 to a.

condenser Il wherein the hydrocarbons are substantially condensed. 'I'hecondensate from the condenser 88 is passed all or in part through theline 8| and recycled by the pump 82 through the line 83 to thefractionator l0. In this way the recycled hydrocarbons are refractioatedalong with the fresh charge so that the isobutane content thereofeventually reaches the alkylation system for further reactionwith olensand for increasing the ratio of isoparaiilns to oleiins.

It is evident that this recycle portion of the ovel'rlld Yfromdebutanizerv85-isrthereby sub1 jected to the depropanizing operationinfractionator Il, thereby preventing propane buildup in the system. v y

It is preferable to withdraw at least a portion of the condensate fromthe condenser 8l through the branch line 84 and -pump 88 to afractionator 88. In the fractionator 88 separation is made between theisobutane and normal butane. The normal butane fraction iswithdrawn as acondensate from the lower portion ofthe fractionator 88 through the line98 and discharged from the system or used, if desired, for increasingthe volatility of stabilized naphthas, for example the stabilizednaphtha withdrawn from the bottom of stabilizer 2. A fraction rich inisobutane is passed from the top of the fractionator 88 through thevapor line 9| to a condenser 92 wherein the hydrocarbons aresubstantially condensed. l'I'he condensate is passed through the line 94to a. pump 95 which recycles the isobutane fraction through the line 96to the line 3,3. for charging along with the fresh olenic charge to theiirst stage of the alkylation system. 'I'he isobutane so recycledincreases the amount of available isobutane for alkylation and also aidsin creating a considerably higher ratio of isobutane to olens in thereaction mixture thanv in the fresh feed to the alkylation system. TheLamount of hydrocarbons charged through the branch line 84 to thefractionator 88 is preferably regof an excess normal butane n-the systemis avoided.

The alkylate is withdrawn from the bottom of .the debutanizer 85 arielpassed through the line 98 to a iractionator |00, wherein the alkylateis separated into the desired fractions. An aviation gasoline ofapproximately 311 F. end lpoint is taken overhead through the vapor linelill and condenser |02. A side stream of `naphtha is withdrawn f rom anintermediate point of the iractionator |00 through the line |03 'to astrinper |04 from which vapors may be returned to the fractionatorthrough vapor line |05. A naphtha of about 300 to 400 F. is withdrawnfrom the bottom of the stripper through the line |06.. The latternaphtha may be used in the manufacture of a heavy aviationor safetyfuel. A fraction heavier than gasoline and boiling isobutane, 13.6 partsisobutylene, 9.9,parts butylabove about 400?. is withdrawn from thebottom of the fractionator through the line |08.

An example will now be given of the operation of the invention althoughit is to be understood that the invention is not limited to the specificexample.

l An unstabilized naphtha from a cracking still is charged to astabilizer from which a stabilized naphtha. an overhead vapor fractioncontaining C3 hydrocarbons, "and a side stream relatively. rich inisobutane, comprising mainly `C4 hydrocarbons with some lighterhydrocarbons, are

withdrawn. 'Iheside 'stream contains about 20 parts isobutane, 5.3 partsisobutylene, 3.8 parts butylene-l, 12 parts n-butane. 4.1 partsbutylene-2 and the remainder lighter yand heavier hydrocarbons. The sidestream is passed to al fractionator wherein the lighter hydrocarbons arefractionated out in order to obtain a more concentratedY C4 fractionfrhebottoms from the fractionator` containing the C4 fraction are mixedy"n-butane, 17.5 parts butylene-2 and the remainder heavier hydrocarbons.The depropanized absorption condensate contains about 9.6 partsisobutane, 7.3 parts isobutylene, 5.4 parts butylene-l.

'- 22.4parts n-butane and 10 parts butylene-2 and the remainder heavierhydrocarbons.

The resulting mixture containing about 46 parts' offractionatedstabilizer side stream. about 174 parts of depropanized debutanizeroverhead` and'about 122 parts of depropanized absorption condensate. arecharged to a debutanizer. 'I'hc mixture charged to the debutanizeranalyzes about 47.6 parts isobutane. 25.5 parts isobntylene, 18.7 partsbutylene-l, 70.9 parts n-butane, 31.6 parts butylene-Z and the remaindermainly heavier hydrocarbons. In the debutanizer a fraction consistingessentially of Ca hydrocarbons. amounting to about 23% of the charge tothe debutanizer, are separated as overhead,`and a lightnaphthacontaining a-portion of the normal butane is withdrawn asbottoms. The debutanizer overhead contains'about 45.2 parts of ene-l,7.1 parts n-butane and 3.2 partsbutylene-2. The overhead fraction iscondensed and the condensate split into approximately equal portionsbetween three allqylation units connected in series. A recycle stream ofisobutane is also charged to the irst stage, whereby a v ratio ofisobutane toolens in the feeds to each stage is at least 5:'1 by volume.I

In each alkylation unit the fresh feed is mixed with a stream of recyclehydrocarbons, principally isobutane, alkylate and sulfuric acid catalystand the mixture passed through a mixer to obtain intimate contact. thenthrough a chiller wherein the heat of reaction is removed by propanerefrigeration. The mixture is passed from the chiller to a reaction tankfrom which the hydrocarbons and catalyst are withdrawn. "The stream sowithdrawn is split. a portion recycled andthe remainder passed tosettler. The ratio of acid to hydrocarbon in the circulating stream isabout 1:1 by volume. The ratio ot strength; sumcient fresh acid is addedto maintain the strength of the acid catalyst at the desired point andan amount of spent acid is withdrawn approximately equal to the amountof the fresh acid added. In the settler the remainder of the acid isseparated from the hydrocarbons and may be recycled to the system o rsent to the next mixing stage.

The crude alkylate withdrawn from the nal settler is neutralizedwithdilute,caustic soda solution and the neutralized hydrocarbons are passedto a debutanizer. An overhead cut from the debutanizer is split into twostreams, a portion being returned to the side cut fractionator,4

referred to heretofore, and the balance going to a butane fractionator.The net normal butane content of the fresh feed is separated in thefractionator and discharged from the system. A recycle stream rich inisobutane taken overhead from the butane fractionator is recycled to thefirst stage of the alkylation system. The bottoms from the debutanizerare charged to a nal fractionator where they are separated byconventional atmospheric distillation into a 311 F. end point overhead,a 311 to 400 F. side cut and bottoms boiling above 400 F. An aviationgasoline of 311 F. end point amounting to approximately 90%, 311 F. to400 F. naphtha, amounting to about 8%, and bottoms boiling above 400 F.amounting to about 2%, are obtained. The aviation gasoline shows anoctane number of about 90, the intermediate naphtha fraction an octanenumber of about 80.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicatedin the appended claims.

We claim:

1. A process for the manufacture of antiknock gasoline, which comprisesstabilizing an unstalbilized cracked naphtha, separating an overheadstream from the stabilizer containing mainly C3 and lighterhydrocarbons, separating a side stream from the stabilizer containing C4oleflns vand paraffns and some Ca hydrocarbons, fracbutane therefrom to.provide a fraction concentrated in isobutane and C4 oleflns, Vsubjectingsaid concentrated isobutane and C4 olen fraction to an alkylationoperation in an alkylation reaction zone wherein isobutane is alkylatedby said olens, separating an unstabilized alkylate from the reactionproducts, stabilizing said separated alkylate to separate normallyliquid alkylate from an overhead fraction consisting. essentially ofisobutane and normal butane, together with any C3 hydrocarbons remainingin the system, recycling a portion of said overhead fraction to the saidside stream fractionating operation to prevent buildup of C3hydrocarbons in the system, fractionating another portion yof saidoverhead to separate an isobutane fraction from a normal butanefraction, and recycling the said isobutane fraction directly to i'zingthe said fractionated C4 stream to separate at least a portion of thenormal butane, thereby increasing the concentration of the isobutane andbutylenes therein, subjecting the debutanized product to alkylation inthe presence of an alkylation catalyst whereby isobutane is alkylated bythe butylenes to produce gasoline hydrocarbons of high anti-knock value,separating unstabilized alkylate from the reaction prodducts,stabilizing said separated alkylate to remove therefrom a light fractionconsisting essentially of isobutane and normal butane together with anyC3 hydrocarbons remaining in the system, and recycling at leasta'portlon of said light fraction to the stabilizer C4 streamfractionating operation to thereby prevent bulldup of C3 hydrocarbons inthe system while maintaining excess isobutane therein.

3. A process for the manufacture of anti-knock gasoline, which comprisesstabilizing an unstabilized cracked naphtha, separating a C4 hydrocarbonstream from the stabilizer containing butylenes, normal butane,isobutane and some C: hydrocarbons, fractionating said stream toseparate C3 hydrocarbons therefrom, debutanizing the 'said fractionatedC4 stream to separate at least a portion of the normal butane therebyincreasing the concentration of the isobutane and butylenes therein,subjecting the debutanlzed product to alkylation in the presence of analkylation catalyst whereby isobutane is alkylated by the butylenes toproduce gasoline hydrocarbons of high anti-knock value, separatingnormally liquid alkylate from the reaction products, also separatingfromthe reaction products a residual gaseous fraction consistingessentially, of isobutane, normal butane and any C; hydrocarbonsretained in the system, recycling a' portion of said residual gaseousfraction to the stabilizer C4 stream fractionating operation to preventbuildup of C3 hydrocarbons in the system while returning isobutane,thereto, fractionating another portion of said residual gaseous fractionto separate a fraction rich in isobutane from a fraction rich in normalbutane, and recycling said fraction rich in isobutane to the alkylationoperation to maintain excess isobutane therein while preventing buildupof normal butane in said system.

4. A process for the manufacture of anti-knock gasoline, which comprisesstabilizing an unstabilized cracked naphtha, separating a C4 hydrocarbonstream from the stabilizer containing bu-` tylenes, normal butane,isobutane and some C: hydrocarbons, fractionatingsaid stream to separateCs hydrocarbons therefrom, debutanizlng the said fractionated C4 streamto separate at least a portion of the normal butane thereby lncreasingtheconcentration or the isobutane and butylenes therein, subjecting thedebutanized product to alkylation in the presence cf an alkylationcatalyst whereby isobutane is alkylated by the butylenes to producegasoline hydrocarbonsof high anti-knock value, separating normallyliquid alkylate from the reaction products, also separating from thereaction products unreacted normally gaseous hydrocarbons consistingessentially of isobutane. and normal butane and any ,Ca hydrocarbonsretained in the system, dividing said unreacted normally gaseoushydrocarbons into separate streams, recycling one stream to thestabilizer C4 fractionating operatlonto prevent buildup f C:hydrocarbons in the system while returning isobutane thereto, subjectinganother stream containing normal butane in an amount .approximating thatin the said debutanized'product fed to the alkylation operation tofractionation to separate an isobutane-rich fraction from a normalbutane fraction. and recycling the isobutane-rich fraction to thealkylation operation to thereby maintain .excess isobutane in the systemwhile preventing buildup vof normal butane therein.

5. A process for the manufacture of anti-knock `gasoline which comprisesstabilizing an unstabilized cracked naphtha,separating a C4 hydrocarbonstream from the stabilizer containing butylenes, normal butane,isobutane and some Ca hydrocarbons, fractionating said stream toseparate Cs hydrocarbons therefrom, debutanizing the saidfractionatedstream to separate at least a portion of the normal butanethereby increasing the concentration of isobutane and butylenes therein,continuously injecting said debutanized product in a circulating streamoi emulsion of hydrocarbons and liquid alkylation catalyst in a closedcircuit in an alkylation `zone wherein isobutane is alkylated by theolens with the production of gasoline hydrocarbons of high antiknockvalue, withdrawing reaction products from the alkylation zone andseparating unstabilized alkylate therefrom; stabilizing said separateda1- kylate to remove a light fraction consisting essentially ofisobutane, normal butaneand any Cs hydrocarbons retained in the system,recycling a portion of said light fraction' to the aforesaid stabilizerC4 fractionating operation to preleasta portion -of the isobutane-richlfraction still gases to remove C3 and lighterhydrocarbons vent buildupof Ca hydrocarbons in the system while retaining the excess isobutanetherein, fractionating another'portion of said light fraction carbon.stream from the stabilizer containing lbutylenes, normal butane,yisobutane and some C: hydrocarbons, fractionating said stream to removeCs hydrocarbons therefrom, debutanizing the said fractionated stream toseparate at least a portion of the normal butane thereby increasing theconcentration of isobutane and butylenes therein, splitting saiddebutanized product into a plurality of streams, separately andsimultaneously passing each stream to separate stages of a multi-stagealkylation system comprising a plurality of serially connectedalkylation zones through which the hydrocarbons undergoing treatment owin series,.and in each of which the hydrocarbons are subjected tocontact-with a liquid alkylation catalyst under conditions such thatisobutane is alkylated by the butylenes to produce vgasolinehydrocarbons of high antiknock value, withdrawing reaction products fromthe final stage of the system and separating unstabiiized alkylatetherefrom, stabilizing said separated alkylate to remove a lightiractionconsisting essentially of isobutane, normal butane and any Cahydrocarbons retained in the system, recycling a portion of .said lightfraction to the aforesaid stabilizer C4 fractionatlng operation toprevent buildup of C3 hydrocarbons in the system lwhile retaining theexcess isobutane therein, separately fractionating another portion ofsaid light fraction to remove an isobutane-rich fraction from a normalbutane fraction, and recycling at directly to the rst stage of saidalkylation system, whereby an excess of isobutane is maintained in saidsystem and flows serially therethrough while buildup of normal butane inthe system is prevented.

7. In the alkylation of isobutane with butylenes vof a normally gaseoushydrocarbon fraction of cracking still gases in the presence of analkylation catalyst for the production of gasoline hydrocarbons of highanti-knock value, the method which comprises fractionati'ng the saidcracking therefrom, and also to remove at least a portion of the normalbutane to providea Cr'fraction concentrated in isobutane and butylenes,subljecting the-said C4 fraction to alkylation with excess isobutane 1inthe presence of an alkylation catalyst under conditions such thatisobutane is alkylated by the butylenes to producegasoline hydrocarbonsof high anti-knock value, separating unstablized alkylate from thereaction products, stabilizing said separated alkylate` to remove anormally gaseous fraction consisting essentially of isobutane and normalbutane with any C3 hydrocarbons retained in the system, and recycling atleast a portion of said normally gaseous fraction to the mst-mentionedfractionating operation of the cracking still gases to thereby preventbuildup of C3 hydrocarbons and normal butane in the system whilemaintaining excess isobutane therein.

8. The method according to claim 7, wherein the said normally gaseousfraction removed in the stabilization of the alkylate is divided intostreams, one stream being recycled to the said fractionating operationof the cracking still gases, and another stream being separatelyfractionated to remove an isobutane-rich fraction from a normal butanefraction, and the said isobutanerich fraction is recycled directly tothe alkylation operation.

9. In the alkylation of isobutane with butylenes of a normally gaseoushydrocarbon fraction of cracking still gases containing C3 and C4hydrocarbons including propane, isobutane, normal butane and butylenesin the presence of an alkylation catalyst for the production of gasolinehydrocarbons of high anti-knock value, the method of handling the saidfraction of cracking still gases without the addition oi extraneouslarge amounts of isobutane which comprises fractionating the saidcracking still gases to separate Ca hydrocarbons and alsoto 'separate asubstantial proportion of the normal butane therefromto thereby obtain aC4V hydrocarbon fraction concentrated in isobutane and butylenes andcontaining only a relatively small proportion of normal butane, theisobutane content of said fraction being in molar excess of the totalolen content thereof, subjecting the said C4 fraction to alkylation inthe presence of an alkylation catalyst under conditions such thatisobutane is alkylated by the .butylenes to produce gasolinehydrocarbons of high anti-knock value, separating an unstabilizedalkylate from. the reaction products, stabilizing said separatedalkylate to remove a normally gaseous fraction consisting essentially ofnormal butane and the excess isobutane together with any C3 hydrocarbonsretained in the system, and recycling at least a portion of the saidnormally gaseous fraction t0 the ilrst-mentioned. fractionatingoperation of the cracking still gases to thereby prevent buildup of C3hydrocarbons and normal butane in the system while maintaining excessisobutane there- 10. The method according to claim 9, wherein the saidnormally gaseous fraction separated in the stabilization of the alkylateis divided into streams, one streambeing recycled to the said crackingstill gas ractionating operation, and another stream being separatelyfractionated to remove an isobutane-rich fraction from a normal lontanefraction, with the said isobutane-rich fraction being recycled directlyto the alkylation operation.

11. In the allrylation of isobutane with butylenes in the presence of analkylation catalyst in a multi-stage system involving serial ilowthrough a plurality of alkylation zones for the production of gasolinehydrocarbons of high anti-knock value, and wherein a Ca-Ci hydrocarbonfraction of cracking still gases containing propane, isobutane,butylenes and normal butane is ernployed as a charge stock, the methodwhich comprises fractionating the said Cs-C4 hydrocarbon fraction toremove C3 hydrocarbons and also to remove a substantial proportion ofthe normal butane therefrom to provide a C4 hydrocarbon fractionconcentrated in isobutane and butylenes, with the isobutane in molarexcess of the butylenes, separately and simultaneously introducingportions of the said C4 fraction into at least two stages of the saidmulti-stage alkylatio'n system whereby isobutane is alkylated bybutylenes in each of said stages to produce gasoline hydrocarbons ofhigh anti-knock value and gasoline hydrocarbons together with excessisobutane ow serially from a preceding stage to a succeeding stage ofsaid system, separating an unstabilized alwlate from the reactionproducts of a final stage of said system, stabilizing said separatedalkylate to remove a normally gaseous fraction consisting essentially ofnormal butane and excess isobutane, fractionating at least a portion ofsaid normally gaseous fraction to separate an isobutane-rich fractionfrom a normal butane fraction, returning another portionof `said normalgaseous fraction to the said Ca-C4 hydrocarbon fractlonating step,recycling the isobutane-rich fraction directly tothe rst stage of thealkylation-system to thereby provide a substantial excess of isobutanewhich ows serially through the multiple stages of said system, -anddischarging the normal butane fraction to remove normal butane from thesystem in an amount comparable to the amount of normal butane introducedwith the C4 hydrocarbon feed into the alkylation system.

l2. A continuous multi-stage process foralkylating a low-boilingisoparailln with an oleiln in the presence of an immlscible liquidalkylation catalyst to produce gasoline hydrocarbons of high anti-knockvalue, which comprises maintaining in' each stage of said multi-stagesysteml a recirculating liquid emulsion stream of catalyst, hydrocarbonreaction products and excess isoparamn in a closed circuit including arestricted now passage and an enlarged reaction zone, splitting theolefin feed between at least two of said stages by simultaneouslyintroducing the olen in liquid phase and in controlled amounts into therestricted flow passage of each of said stages under conditions suchthat the isoparailln is maintained in substantial molarexcess in each ofsaid stages and isoparamn is alkylated with the oleiln to producegasoline hydrocarbons of high anti-knock value as the emulsion streamcirculates through the restricted ow passage and enlarged reaction zone,continuously removing a small portion of the recirculating emulsionstream from each stage, 'passing hydrocarbon reaction products andexcess isoparafiin of the removed stream from a prior stage andintroducing the same linto the recirculating emulsion stream of asubsequent stage whereby the hydrocarbon reaction products ',and excessisoparailln ow serially through said stages, continuously separatingexcess isoparan from hydrocarbon reaction products removed from thefinal stage, dividing said excess isoparailln separatedfrom hydrocarbonreaction products, recycling one portion of `said excess-isoparain tothe recirculating emulsion stream of the first-mentioned stage tothereby 'assist in maintaining the said substantial molar excess ofisoparaflin in said stages, and adding another portion of said separatedexcess isoparaiiln'to the oleiin feed which is then iractionated toremove propane and ultimately split between said stages.

FRANCIS HORTON.

LEBBEUS C. KEMP. RICHARD E. NAGLE. LOREN P. SCOVILLE.

